Those who used languages besides Mandarin in class or on the playground had signs hung round their necks that said, “I love speaking guóyǔ,” and were punished with beatings and fines.

All this abruptly changed when Japan relinquished control of Taiwan back to China at the end of World War II. Across the strait, China was slipping into civil war between Chiang Kai-shek’s Nationalist Kuomintang and Mao Zedong’s Communist forces. In 19...